ConvertHandle.h

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#ifndef DataFormats_Common_ConvertHandle_h
#define DataFormats_Common_ConvertHandle_h

#include "DataFormats/Common/interface/BasicHandle.h"
#include "DataFormats/Common/interface/Handle.h"
#include "DataFormats/Common/interface/Wrapper.h"
#include "FWCore/Utilities/interface/Likely.h"

#include <typeinfo>
#include <algorithm>
#include <memory>

namespace edm {

  namespace handleimpl {
    void throwConvertTypeError(std::type_info const& expected, std::type_info const& actual);
    std::shared_ptr<edm::HandleExceptionFactory> makeInvalidReferenceException();
  }

  // Convert from handle-to-void to handle-to-T
  template<typename T>
  Handle<T> convert_handle(BasicHandle && bh) noexcept(true) {
    if UNLIKELY(bh.failedToGet()) {
      return Handle<T>(std::move(bh.whyFailedFactory()));
    }
    void const* basicWrapper = bh.wrapper();
    if UNLIKELY(nullptr == basicWrapper) {
      return Handle<T>{handleimpl::makeInvalidReferenceException()};
    }
    auto wrapper = static_cast<Wrapper<T> const*>(basicWrapper);

    return Handle<T>(wrapper->product(), bh.provenance());
  }
  
  template<typename T>
  Handle<T> convert_handle_check_type(BasicHandle && bh) {
    if UNLIKELY(bh.failedToGet()) {
      return Handle<T>(std::move(bh.whyFailedFactory()));
    }
    void const* basicWrapper = bh.wrapper();
    if UNLIKELY(basicWrapper == nullptr) {
      return Handle<T>{handleimpl::makeInvalidReferenceException()};
    }
    if UNLIKELY(!(bh.wrapper()->dynamicTypeInfo() == typeid(T))) {
      handleimpl::throwConvertTypeError(typeid(T), bh.wrapper()->dynamicTypeInfo());
    }
    Wrapper<T> const* wrapper = static_cast<Wrapper<T> const*>(basicWrapper);
    
    return Handle<T>(wrapper->product(), bh.provenance());
  }

}

#endif